<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>

<body>
    <script>
        var a = 10;
        var b = 20;

        function fun() {
            var c = 30;

            function inner() {
                var a = 40;
                var d = 50;
                console.log(a, b, c, d); //40 20 30 50
            }
            inner();
        }

        fun();
    </script>
</body>

</html>